Effect of hydrogen peroxide and carbon-to-nitrogen ratio on growth and biochemical profile in oleaginous Mucoromycota

Background Hydrogen peroxide (H₂O₂) plays a crucial role in biology of both redox reactions and oxidative stress. In some ranges of concentrations, H₂O₂ can work as a signaling molecule, triggering specific metabolic pathways. Some works have explored the influence of H₂O₂ and other stress molecules in lipid accumulation. Additionally, H₂O₂ has gained attention as cofactor of lytic polysaccharide monooxygenases (LPMOs) during lignocellulose saccharification. The action of these enzymes demonstrated to enhance significantly the saccharification efficiency. However, in simultaneous saccharification and fermentation (SSF) processes H₂O₂ can have deleterious effects on the fermenting microorganism. In this study, nine strains from eight different species of Mucoromycota were grown at different sublethal concentrations of H₂O₂ and two carbon-nitrogen (C/N) ratios. The aim of this study was to investigate if H₂O₂ could be used in Mucoromycota SSF processes and to identify which possible effects, beneficial or deleterious, could occur under different C/N conditions. Results In general, all the strains tolerated H₂O₂ at much higher concentrations than those commonly used to improve enzymatic saccharification (1-19 mM vs 1-240 µM). Infrared spectroscopy was used to analyze the biochemical composition of the fungi. The exposure to sublethal H₂O₂ doses did not increase any metabolite in particular but slightly reduced biomass production at concentrations near the minimal inhibitory concentration (MIC) in some cases. For Lichtheimia corymbifera grown in standard C/N medium, an accumulation of intracellular proteins with oxidative damage was positively correlated to the H₂O₂ concentration. This was not observed for other strains. The biggest changes in the biochemical composition of the fungal biomass were linked to changes in medium C/N ratios. This included different carbon allocation strategies among the tested species, such as allocation towards lipids and polyphosphates, lipids and saccharides, etc. Conclusions Our results suggest that the Mucoromycota strains here are compatible with H₂O₂ feeding in lignocellulose-based SSF to enhance efficiency while sustaining minimal oxidative damage.